Remove extern C blocks from lib/* internal APIs (except xxhash.h)

lib/common/threading.h

@@ -56,11 +56,6 @@
 #define ZSTD_pthread_cond_signal(a)     WakeConditionVariable((a))
 #define ZSTD_pthread_cond_broadcast(a)  WakeAllConditionVariable((a))
 
-
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 /* ZSTD_pthread_create() and ZSTD_pthread_join() */
 typedef HANDLE ZSTD_pthread_t;
 
@@ -73,20 +68,10 @@ int ZSTD_pthread_join(ZSTD_pthread_t thread);
  * add here more wrappers as required
  */
 
-
-#if defined (__cplusplus)
-}
-#endif
-
 #elif defined(ZSTD_MULTITHREAD)    /* posix assumed ; need a better detection method */
 /* ===   POSIX Systems   === */
 #  include <pthread.h>
 
-
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 #if DEBUGLEVEL < 1
 
 #define ZSTD_pthread_mutex_t            pthread_mutex_t
@@ -133,17 +118,9 @@ int ZSTD_pthread_cond_destroy(ZSTD_pthread_cond_t* cond);
 
 #endif
 
-#if defined (__cplusplus)
-}
-#endif
-
 #else  /* ZSTD_MULTITHREAD not defined */
 /* No multithreading support */
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 typedef int ZSTD_pthread_mutex_t;
 #define ZSTD_pthread_mutex_init(a, b)   ((void)(a), (void)(b), 0)
 #define ZSTD_pthread_mutex_destroy(a)   ((void)(a))
@@ -159,10 +136,6 @@ typedef int ZSTD_pthread_cond_t;
 
 /* do not use ZSTD_pthread_t */
 
-#if defined (__cplusplus)
-}
-#endif
-
 #endif /* ZSTD_MULTITHREAD */